The present invention relates to a new and improved construction of apparatus for damping the pressure increase of hydrostatic drives wherein a controllable axial piston pump, preferably equipped with a swash or wobble plate, drives a motor or selectively the hydraulic cylinder of a concrete pump.
With such type drives oftentimes there occur rapid load changes at the motor, even if such operates at a constant rotational speed. In the case of concrete pumps operating according to a rotor principle or piston displacement principle, such is the case if, after each stroke change or after each operable activity of a displacement roller, the concrete column, which is at rest during the stroke change in the conveying line, again must be accelerated. The rotational movement of the oil motor or the speed of the piston rods of the conveying cylinder is always a uniform one because it is acted upon by a displacement pump.
The large forces required for the renewed acceleration of the concrete column leads to a brief high pressure increase at the high pressure side of the drive. The pressure peaks are so high that the overpressure valve responds and there is perceivable a certain development of heat. On the other hand, the sudden accelerated concrete column produces undesirable reaction forces which, for instance, can result in the concrete line or conduit being exposed to impacts.
In order to overcome these drawbacks it would be conceivably possible, after each stroke reversal or change, to rock the hydraulic pump into its null conveying position and to allow such to be slowly controlled in order to realize a slow feed of the concrete column. Yet in practice this is not possible for a number of reasons, particularly also because the time-span between the point in time of reversing the control of the conveying pistons and the moment at which such impinge against the concrete columns and begin to accelerate such occur quite differently, depending upon the composition of the concrete and the operating speed of the pump.
To avoid such acceleration peaks which oftentimes exceed 200% of the conveying pressure, it is equally not possible to employ the known pressure compensation. During conveying of the concrete the pressure level continuously changes because the consistency of the concrete and the length of the conveying conduit or line varies.